1. Field of the Invention
The present invention relates generally to imaging systems, and more particularly but not exclusively to light modulator arrays.
2. Description of the Background Art
A micro electromechanical system (MEMS), such as light modulators, typically includes micromechanical structures that may be actuated using electrical signals. Examples of MEMS light modulators include the Grating Light Valve™ (GLV™) light modulators available from Silicon Light Machines, Inc. of Sunnyvale, Calif. GLV-type light modulators typically include an array of moveable structures referred to as “ribbons.” GLV-type light modulators are also referred to herein as “ribbon light modulators.”
Light modulators, in general, may be employed in various applications including video, printing, and optical switching, for example. Light modulators may also be employed in so-called “maskless lithography” where a mask and/or reticle can be replaced by a dynamic direct writing process using light modulators. Such a system could speed up chip design cycle times and reduce cost, particularly with respect to design changes, which would previously require one or more new masks to be made for each design revision. Similar systems can also be used in patterning masks.
FIGS. 1-4 show schematic diagrams of example maskless lithography systems. In the maskless lithography system of FIG. 1, a deep ultraviolet (DUV) laser 150 provides an optical source through conditioning and illumination optics 151 and onto a light modulator device 152 that is controlled by data input and drivers 153 according to an associated image database 160. Image database 160 comprises a plurality of pixels of a two-dimensional pattern or image. Light modulated by the modulator device 152 goes through relay optics and Fourier filter 154, an intermediate image plane 155, projection optics 156, and on to the wafer 157. The wafer 157 is scanned relative to the light beam by a movable wafer stage 158. With this system, “swaths” or lines can be imaged on the wafer surface and, using photosensitive layers, as in conventional lithography, patterns can be exposed on the wafer surface.
The maskless lithography system of FIG. 2 employs a scanned linear (i.e., one-dimensional) light modulator array 172. Illumination from a light source 131 is modulated by modulator array 172 onto an Offner relay 173. From Offner relay 173, the modulated light is projected on the wafer 176 by way of an intermediate image plane 174 and projection lens 175.
FIG. 3 schematically illustrates how an image modulated by a linear light modulator array may be scanned onto a wafer. In the maskless lithography system of FIG. 3, a laser 181 serves as a light source. Light from laser 181 is modulated by a linear light modulator device 183 by way of beam shaping optics 182. Light modulator device 183 modulates incident light in accordance with an image stored in an image computer 184. The modulated light passes through reduction lens 136 and onto a wafer 185. Because it comprises a one-dimensional array of light modulators, light modulator device 183 projects the image onto wafer 185 one column of pixels at a time. Wafer 185 is scanned (e.g., using a wafer stage) relative to linear light modulator device 183 to project the entire image onto the wafer.
A one-dimensional maskless lithography system, such as that employed in the systems of FIGS. 2 and 3, is limited in the number of pixels that can be written at a single time. This problem can be overcome by using a two-dimensional light modulator array. A two-dimensional light modulator array allows for the writing of more than one column of pixels at a time. For example, as shown in the maskless lithography system of FIG. 4, illumination from a light source 191 may be projected on a two-dimensional light modulator array 193 by way of collimating lens 198 and microlens array 90. Microlens array 90 focuses the light beam on the modulating elements of modulator array 193. Light modulator array 193 modulates incident light onto a wafer 197 by way of an Offner relay 194, a prism 189, microlens array 171, an intermediate plane 195, and projection lens 196. The Offner relay 194 is a reflective optical device that is composed of two reflecting mirror elements 187 and 186. The Offner relay 194 effectively performs Fourier transform and inverse Fourier transform functions to accomplish a one-to-one imaging relationship with an intermediate Fourier plane located at the surface of element 186. A filter can be added at the element 186 location to perform Fourier filtering. Thus, element 186 serves as both a mirror and a Fourier plane filter. The Offner relay 194 is used here as a generic example of a Fourier optics filtering system. Equivalently, other types of reflective or refractive optical components may also be used to perform this function. The component (i.e., order) of the modulated light not filtered out by the Fourier plane filter function of element 186 reaches a prism 189 by way of mirror element 187. Prism 189 directs the modulated light onto microlens array 171, which focuses the light onto an intermediate image plane 195 and projection lens 196. The modulated light reaches wafer 197 underneath projection lens 196 to print a pattern thereon.
Other lithography systems are also disclosed in U.S. Pat. No. 6,379,867 to Mei et al., U.S. Pat. No. 6,473,237 to Mei, U.S. Pat. No. 6,312,134 to Jain et al., U.S. Pat. No. 5,900,637 to Smith, U.S. Pat. No. 6,133,986 to Johnson, and U.S. Publication No. 2002/0092993 by Kanatake et al., all of which are incorporated herein by reference in their entirety.
The modulator arrangements of the aforementioned maskless lithography systems may include one-dimensional and/or two-dimensional configurations of tightly-packed modulators. That is, the modulators substantially have the same spacing or pitch in both dimensions. A characteristic of tightly-packed modulators is that the modulators may interact optically and often coherently. While this may not be a problem in systems where such interacting modulators map to ultimate pixels that will be adjacent to each other, such as in display systems, it is not advantageous for systems without such mapping. For example, in systems where adjacent modulators on the light modulator array form and/or map to non-adjacent pixels on the ultimate image or lithographic target, such a tightly-packed modulator arrangement is not optimal. Thus, a two-dimensional light modulator array arrangement capable of supporting an adjacent to non-adjacent modulator mapping for optimal optical resolution is generally desirable.